This invention is in the field of dehumidification and in particular is concerned with improved efficiency of desiccant type dehumidifiers.
Large scale air dehumidifying systems based on a desiccating agent are associated with two main problems. One problem is that the dried air output is warmer than the moist air input. This result is caused by the heating of the air from latent heat of evaporation as the moisture is removed therefrom and also, to a lesser degree by the heating of the air by transfer of heat from the generally warmer desiccant. A second problem is that regeneration of the desiccant requires considerable energy.
Dehumidifying systems based on liquid desiccants dehumidify air by passing the air through a tank filled with desiccant. The moist air enters the tank via a moist air inlet and dried air exits the tank via a dried air outlet. In one type of desiccant system a shower of desiccant from a reservoir is sprayed into the tank and, as the desiccant droplets descend through the moist air, they absorb water from it. The desiccant is then returned to the reservoir for reuse. This causes an increase in the water content of the desiccant.
Water saturated desiccant accumulates in the reservoir and is pumped therefrom to a regenerator unit where it is heated to drive off its absorbed water as vapor. Regenerated desiccant, which heats up in this process, is pumped back into the reservoir, for reuse. Since the water absorption process leads to heating of the air and the regeneration process heats the desiccant, substantial heating of the air takes place during the water absorption process.
An example of a device using a circulating hygroscopic liquid such as a LiCl desiccant is described in U.S. Pat. No. 4,939,906. In this patent a boiler is provided with finned tubes for the flow of the heated desiccant. This patent also discloses pre-heating the saturated desiccant before it enters the boiler for final regeneration by direct transfer of heat thereto from desiccant leaving the tank.
Other variations of systems using re-circulated desiccant solutions for dehumidifying air are shown in U.S. Pat. Nos. 4,635,446, 4,691,530 and 4,723,417. Many of these systems utilize transfer of heat from one portion of the dehumidifier to another to improve its efficiency.
In general, regeneration of the liquid desiccant requires its heating with the concomitant expenditure of energy.
The present invention, in some embodiments thereof, is designed to utilize heat transfer in a new way in the process of regenerating its liquid desiccant thereby enhancing the overall efficiency of the system.
In a preferred embodiment of the invention a heat pump extracts heat from liquid desiccant, preferably in a humidity collector unit and transfers the heat to a heating coil in a regenerator unit thereby reducing the overall energy required by the system. In addition, this transfer of energy has the effect of cooling the desiccant which contacts the moist air that enters the system. Thus, dry air which exits the system is cooler than it would be in the absence of the heat transfer.
In addition, in preferred embodiments of the invention, heat energy in one or more of moisture laden air which exits the regenerator, heated desiccant which exits the regenerator and air which exits the dehumidifier is used to heat the desiccant to be regenerated either on its way to or in the regenerator tank.
According to an aspect of some preferred embodiment of the invention, a dehumidifier is provided in which the relative humidity of treated air is self regulating, such that the relative humidity of the air exiting the dehumidifier remains relatively constant as the temperature or humidity of the air entering the dehumidifier drops. The air temperature of the exiting air preferably depends on the input air conditions, with the exit air temperature dropping with lower input_temperature/relative humidity. There is thus provided, in accordance with a preferred embodiment of the invention, a dehumidifier system comprising:
a dehumidifying chamber into which moist air is introduced and from which less moist air is removed after dehumidification;
a desiccant solution situated in at least one reservoir;
a first conduit via which desiccant solution is transferred from the at least one reservoir to the dehumidifying chamber, said solution being returned to said at least one reservoir after absorbing moisture from the moist air;
a regenerator which receives desiccant solution from said at least one reservoir and removes moisture from it;
a second conduit via which desiccant is transferred from the at least one reservoir to the regenerator, said solution being returned to said at least one reservoir after moisture is removed from it; and
a heat pump that transfers heat from the solution in the first conduit to the solution in the second conduit.
Preferably, the heat pump comprises a first heat exchanger which receives heat from the solution in the first conduit, a second heat exchanger that receives heat from the solution in the second conduit and a compressor.
Preferably, the regenerator comprises a regenerator chamber in which moisture is removed from the solution by contact with air that is brought into the chamber. Preferably, the compressor is cooled by said air prior to its entry into the regenerator chamber, such that the moisture removal ability of the air is increased.
In a preferred embodiment of the invention, the heat pump includes an additional heat exchanger which transfers heat from a refrigerant after the refrigerant leaves the second heat exchanger. Preferably, the regenerator comprises a regenerator chamber in which moisture is removed from the solution by contact with air that is brought into the chamber. Preferably, the additional heat exchanger is cooled by said air prior to its entry into the regenerator chamber, such that the moisture removal ability of the air is increased.
In a preferred embodiment of the invention, the system includes a control that controls the amount of heat transferred by the heat pump.
In a preferred embodiment of the invention, the at least one reservoir comprises a first reservoir from which solution is transferred via the first conduit and a second reservoir from which solution is transferred via the second conduit. Preferably, a substantial temperature differential is maintained between the first and second reservoirs.
Preferably, the system includes a conduit that connects the first and second reservoirs, such that the level of solution in them is substantially the same.
There is further provided, in accordance with a preferred embodiment of the invention, a dehumidifier system comprising:
a dehumidifying chamber into which moist air is introduced and from which less moist air is removed after dehumidification;
a desiccant solution situated in a first reservoir;
a first conduit via which desiccant solution is transferred from the first reservoir to the dehumidifying chamber, said solution being returned to said at least one reservoir after absorbing moisture from the moist air;
a desiccant solution situated in a second reservoir;
a regenerator which receives desiccant solution from the second reservoir and removes moisture from it;
a second conduit via which desiccant is transferred from the second reservoir to the regenerator, said solution being returned to said second reservoir after moisture is removed from it; and
wherein a substantial temperature differential is maintained between the first and second reservoirs.
Preferably, the system includes a conduit connecting the first and second reservoirs such that the level of solution in them is substantially the same.
Preferably, the conduit provides for only limited mixing between the two reservoirs such that the substantial temperature differential is maintained between them. Preferably, the temperature differential is at least 5xc2x0 C., such as at least 10xc2x0 C. or at least 15xc2x0 C.
Preferably, the system includes means for providing an additional limited amount of mixing between the two reservoirs.
There is further provided, in accordance with a preferred embodiment of the invention, an air modifying device, including:
an enclosure including apparatus for modifying air entering the apparatus via an air inlet and having an air outlet for the modified air;
a first conduit having an entrance for air and an exit communicating with the inlet;
a second conduit having an exit and an entrance communicating with the outlet; and
a mounting surface adapted for mounting the device on a partition such that the enclosure is on a first side of the partition and the entrance to the first conduit and the exit from the second conduit are situated on a second side of the partition.
Preferably, the conduits carry air from the first side of the partition to the second side of the partition. Preferably, the mounting surface is adapted for mounting on a window sill and the system includes a seal around the conduits that seals the first side of the partition from the second side of the partition when a window is closed on the conduits.
In a preferred embodiment of the invention, the apparatus for modifying air is a dehumidifier.
In a preferred embodiment of the invention, the apparatus for modifying air is an air conditioner including a heat pump that cools air entering the inlet by contact with a cold surface of the heat pump.
In a preferred embodiment of the invention, the apparatus for modifying air is a combination dehumidifier and an air conditioner including a heat pump that cools air entering the inlet by contact with a cold surface of the heat pump.
In a preferred embodiment of the invention, the dehumidifier is a dehumidifier system as described herein.